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Geothermal ground source/water source heat exchange systems typically include fluid-filled closed loops of tubing buried in the ground, or submerged in a body of water, that either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged fluid transport tubing. The tubing loop is extended to the surface and is then used to circulate the naturally warmed or cooled fluid to an interior air heat exchange means.
Common and older design geothermal water-source heating/cooling systems typically circulate, via a water pump, a fluid comprised of water, or water with anti-freeze, in plastic (typically polyethylene) underground geothermal tubing so as to transfer geothermal heat to or from the ground in a first heat exchange step. Via a second heat exchange step, a refrigerant heat pump system transfers heat to or from the water. Finally, via a third heat exchange step, an interior air handler (comprised of finned tubing and a fan) transfers heat to or from the refrigerant to heat or cool an interior air space.
More recent geothermal DX heat exchange systems have refrigerant fluid transport lines placed directly in the sub-surface ground and/or water. These systems typically circulate a refrigerant fluid, such as R-22, R-410a, or the like, in the sub-surface refrigerant lines, which are typically comprised of copper tubing, to transfer geothermal heat to or from the sub-surface elements via a first heat exchange step. DX systems only require a second heat exchange step to transfer heat to or from the interior air space, typically by means of an interior air handler. Consequently, DX systems are generally more efficient than water-source systems because less heat exchange steps are required and because no water pump energy expenditure is necessary. Further, since copper is a better heat conductor than most plastics, and since the refrigerant fluid circulating within the copper tubing of a DX system generally has a greater temperature differential with the surrounding ground than the water circulating within the plastic tubing of a water-source system, generally, less excavation and drilling is required, and installation costs are lower, with a DX system than with a water-source system.
While most in-ground/in-water DX heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Several such design improvements, particularly in direct expansion/direct exchange geothermal heat pump systems, are taught in U.S. Pat. No. 5,623,986 to Wiggs; in U.S. Pat. No. 5,816,314 to Wiggs, et al.; in U.S. Pat. No. 5,946,928 to Wiggs; and in U.S. Pat. No. 6,615,601 B1 to Wiggs, the disclosures of which are incorporated herein by reference. Such disclosures encompass both horizontally and vertically oriented sub-surface heat geothermal heat exchange means.
The known geothermal heat exchange systems suffer from the following drawbacks:
(1) As DX systems are switched from the heating mode to the cooling mode at the end of a heating season (i.e., when the ground is cold and the refrigerant within the interior heat exchanger, such as an air handler, is at a temperature at or below freezing), it is difficult to obtain a full design refrigerant flow through the system, and the interior heat exchange refrigerant transport tubing tends to “frost,” thereby decreasing system operational efficiencies;
(2) The current means for insulating the liquid refrigerant transport line in a sub-surface environment are inadequate; and
(3) The refrigerant transport lines are often placed in a sub-surface environment that is corrosive to metal, such as commonly-used copper, and therefore a means for protecting the refrigerant transport lines from corrosion is desirable.
Consequently, a means to provide at least one of full and close to full design refrigerant flow and a means to prevent “frosting” of the interior refrigerant transport heat exchange tubing in a DX system when changing from the heating mode to the cooling mode would be preferable; improvements to insulating the liquid refrigerant transport line in a sub-surface environment mode would be preferable; and a means of protecting all refrigerant transport lines in a sub-surface environment that is corrosive to metal, such as copper for example would be preferable. The present disclosure provides a solution to these preferable objectives, as hereinafter more fully described.